Halogen vapor detector



Oct. 20, I970 HANS-GEORG ZIMMERMANN 3,535,088

HALOGEN VAPOR DETECTOR Filed June 16, 1967 2 Sheets-Sheet 1 Oct. 20, 1970 HANSGEORG ZIMMERMANNI HALOGEN VAPOR DETECTOR 2 Sheets-Sheet 2 Filed June 16, 1967 United States Patent 3,535,088 HALOGEN VAPOR DETECTOR Hans-Georg Zimmermann, Uberlingen (Bodensee), Germany, assignor to Bodenseewerk Perkin-Elmer 81 C0., G.m.b.H., Uberlingen (Bodensee), Germany, a corporation of Germany Filed June 16, 1967, Ser. No. 646,629 Claims priority, application Germany, July 1, 1966, B 87,813; Oct. 21, 1966, B 89,488 Int. Cl. G01n 27/62 U.S. Cl. 23-254 12 Claims ABSTRACT OF THE DISCLOSURE A halogen detector includes an enclosed body forming a reservoir for an alkali material. The body includes a portion formed of a material which is permeable to vapor of the alkali material. A heater means is adapted for causing the alkali material to vaporize and thereby diffuse through the permeable material. Means, including first and second electrodes positioned near said permeable material, establish an electric field and indicate the amplitude of current flow in the presence of a halogen vapor.

This invention relates to arrangements for detecting the presence of halogen vapors and vapors of halogen compounds.

In one form of a halogen vapor detector, the halogen vapor flows between two electrodes, one of which is heated. The heated electrode comprises a body sensitized with an alkali compound and which ,is pervious to the alkali. Positive ions are liberated at the heated electrode in the presence of the halogen, the number of such liberated ions increasing as the halogen vapor concentration increases. An electric potential is applied between the electrodes and a meter coupled to the electrodes provides an output indication of the halogen vapor concentration. A halogen vapor detector of this type is described in German patent specification 907,223.

A further halogen detector of this type has been proposed wherein a ceramic body is impregnated with the alkali compound and the electrodes comprise a first coil of wire positioned in an aperture of the body and a second coil of wire arranged centrally in the aperture. The operation of the detector causes a depletion of the alkali compound over a period of time and a diffusion of the alkali from the body varies accordingly. As a result, an undesired change occurs in the base line of an output signal and in the sensitivity of the detector.

Accordingly, it is an object of the present invention to provide an improved form of halogen vapor detection apparatus.

Another object of the invention is to provide a halogen vapor detector of the general type described which is adapted for operation over relatively long periods of time with substantially consistent sensitivity.

In accordance with the present invention, a halogen vapor detector comprises a hollow body defining a container for an alkali compound and wherein at least a portion of said body is formed of an alkali permeable material. An alkali compound is positioned in the container and means are provided for heating and causing the alkali compound to vaporize. Means, including first and second electrodes positioned near the permeable material, are provided for establishing an electric field and for indicating ion current flow. Thermal decomposition of the alkali compound occurs gradually by virtue of the heating and the products of decomposition diffuse through the permeable portion into the space between the electrodes. Thus, a relatively large supply of alkali compound is 3,535,088 Patented Oct. 20, 1970 provided rather than an impregnated ceramic body wherein the alkali is contained only in the pores of the ceramic body. The detector sensitivity and output signal baseline are thereby maintained substantially constant over a relatively long period of time.

These and other objects of the present invention will become apparent with reference to the following specifications and drawings wherein:

FIG. 1 illustrates an embodiment of the invention;

FIG. 2 is a sectional view of another embodiment of the invention;

FIG. 3 illustrates a body for containing an alkali compound;

FIG. 4 illustrates a detector arrangement adapted for use with the body of FIG. 3;

FIG. 5 illustrates still another detector arrangement adapted for use with the body of FIG. 3; and

FIG. 6 illustrates an alternative arrangement of the detector of FIG. 1.

Referring now to FIG. 1, there is illustrated a porous ceramic body 10 of generally cylindrical shape having a hollow space 11 or cavity containing a supply of an alkali compound. K Cr O or KMnO, are exemplary materials suitable for use as the alkali compound. The hollow body 10 is closed by a cover 12 which can be removed in order to replenish the supply of alkali material. A coil 13 is positioned about the body 10. This coil functions both as one electrode of the halogen detector and as a heater. A heater voltage is applied to this coil and causes a heating current to flow therein. The supply of alkali compound in hollow space 11 is thermally decomposed gradually by virtue of the heating and the alkali is caused to diffuse outwardly through the porous ceramic hollow body 10. A chemical equilibrium is established in the hollow space at which a specific vapor pressure of the products of decomposition (alkali and residual compound) is produced as long as a supply of alkali compound is still present. The alkali diffuses through the body 10 to one electrode and substantially constant conditions are maintained over a period of time as long as there remains a supply of alkali compound in the hollow space. The ceramic hollow body 10 with coil 13 is surrounded by a wire mesh or netlike collecting electrode 14 in spaced-apart relationship. A voltage is applied between coil 13 and the collecting electrode 14 from a source 15 in series with a signal amplifier 16. A sample under investigation flows from a source to the detector. Alternatively, the detector may be positioned in an atmosphere to determine the presence of halogen vapors. Positive ions are created in accordance with the halogen vapor concentration. A resulting output current is amplified by amplifier 16 and indicating or recording means, not illustrated, are employed for providing an output indication.

In the embodiment of FIG. 2 a ceramic body 17 is provided with a central aperture 18. One electrode is formed by a coil of wire 19 abutting the inner wall of aperture 18. The other electrode 20 is arranged centrally in aperture 18. The gas to be analyzed is passed through the aperture 18. The ceramic body 17 is surrounded by a hollow space 21 which is defined between the ceramic body 17 and an outer jacket 22. In the hollow space 21 there is also arranged a supply of alkali compound. On the inner wall of jacket 22 there is provided a heating coil 23, whereby a thermal decomposition of the alkali compound and a diffusion of the alkali is effected inwardly into the aperture 18.

In FIG. 3 the hollow body is shown to comprise an elongated platinum tube 24 of relatively small diameter which is filled with alkali and closed at the ends thereof. The tube can be of capillary dimensions. It has demonstrated the characteristic that the alkali atoms diffuse through the body along the grain boundaries of the platinum tube. In a particularly advantageous arrangement, the platinum body of FIG. 3 contains carbon in addition to the alkali material. Because of the presence of the carbon, the grain-boundaries of the platinum are expanded and the diffusion of the alkali therethrough is facilitated. An exemplary material contained by the tube is a mixture of graphite and an alkali compound. A decomposable carbonaceous alkali compound provides an advantageous filling material. Alkali alcoholate has proven to be a suitable material. The carbon is then produced as a product of decomposition of the alkali compound.

In the embodiment according to FIG. 4 the filled platinum tube 24 of FIG. 3 is bent to form a coil 25 which is mounted on a burner nozzle 26 on which a hydrogen flame 27 is burning. The hydrogen is supplied via a line 28. The coil 25 is mounted in the oxidizing portion of the flame and is heated thereby. Coil 25, nozzle 26 and line 27 constitute one electrode of the detector. Above the flame-or thereaboutthere is arranged a counter-electrode 29. A voltage is applied between electrode 29 and line 28 from a source 30 through a signal amplifier 31. The sample gas is introduced in the direction of the arrows from below.

FIG. 5 illustrates a flame ionization detector 51 comprising an additional arrangement for measuring or determining halogen vapors. A mixture of sample gas, car- 'rier gas (in gas chromatography) and hydrogen is introduced through a line 32. This mixture is burned in a flame 33 adjacent a nozzle 34. The flame 33 is surrounded by a counterelectrode 35 in jacket-like manner. A voltage source 36 and a signal amplifier 37 is coupled between nozzle 34 which constitutes one electrode, and the counterelectrode 35. The signal amplifier supplies a signal I, which is the normal flame ionization detector signal. For detecting and measuring halogen vapors there is provided a second device generally referenced as 38 above the flame ionization detector. This second device contains a coil 39 of a platinum tube filled with alkali. However, this one is not heated by a flame in the manner of FIG. 4, but is heated by applying an AC. voltage to the ends 40 thereof. A voltage source 42 and signal amplifier 43 are coupled between coil 39 and a counterelectrode 41. The amplifier 43 supplies a signal II which is specific for halogen vapors which rise together with the combustion gases of the flame ionization detector upwardly through coil 39.

FIG. 6 illustrates an alternative arrangement of the detector of FIG. 1. Equivalent parts in FIG. 1 and FIG. 6 are provided with the same reference characters. One electrode 44 protrudes into the hollow space filled with alkali, which electrode is connected with the heating coil 13 acting as electrode via a voltage source 45. In this manner, the diffusion of alkali outwardly can be adjusted electrolytically in accordance with the potential applied to electrode 44.

While I illustrated and described particular embodiments of my invention, it will be understood that various modifications may be made therein without departing from the spirit of the invention.

I claim:

1. In a flame ionization detector having a burner nozzle, an electrode member, means for establishing an electric potential between said nozzle and said electrode and for indicating current flow therebetween, means for conducting a combustible gas and a sample to flow to said nozzle for burning said sample and forming a flame thereby, the improvement comprising an elongated alkali vapor permeable platinum capillary tubulation of relatively narrow cross section sealed at opposite ends thereof, and containing an alkali compound, said tubulation formed in a coil configuration and disposed with respect to said nozzle in a manner for causing said flame to heat said tubulation.

2- n a flame ionization detector having a burner nozzle, an electrode member, means for establishing an electric potential between said nozzle and said electrode and for indicating current flow therebetween, means for conducting a combustible gas and a sample to said nozzle for burning said sample to thereby provide combustion products, the improvement comprising an elongated alkali vapor permeable platinum capillary tubulation of relatively narrow cross section sealed at opposite ends thereof and containing an alkali compound and a second electrode disposed in a flow path of said combustion products, electrical circuit means for causing an electric current to flow in said tubulation heating said tubulation, means for establishing an electric field and for indicating current flow between said tubulation and said second electrode.

3. A halogen vapor detector comprising:

an enclosed body defining a container for an alkali compound;

said body including a portion thereof formed of a material which is permeable to vapors of an alkali compound;

said body including an inner tubular member formed of said permeable material;

an alkali compound positioned about said inner tubular member;

heater means comprising a heater coil formed about said alkali compound for causing said compound to vaporize and to thereby diffuse through said alkali permeable material; and,

means, including first and second spaced-apart electrodes positioned within said tubular member for establishing in a space between said electrodes an electrical field and for indicating current flow between said electrodes, said body positioned with respect to said electrodes for providing introduction of diffusion of alkali vapors into the space between said electrodes, thereby enhancing current flow between electrodes in the presence of a halogen vapor.

4. A halogen vapor detector comprising:

an enclosed body defining a cavity for containing an alkali compound;

an alkali compound positioned in said cavity of said body;

said body including a portion thereof formed of a material which is permeable to vapors of the alkali compound;

heater means adapted for causing said alkali compound to vaporize and to thereby diffuse through said alkali permeable material;

said enclosed body including demountable means providing access to said cavity for replenishing said compound when said compound is depleted by vaporization;

means, including first and second spaced-apart electrodes for establishing an electric field in a space between said electrodes and for indicating current flow between said electrodes, said body positioned with respect to said electrodes for providing introduction of diffusing alkali vapor into the space between said electrodes thereby enhancing current flow between the electrodes in the presence of a halogen vapor.

5. A detector in accordance with claim 4 including means defining a flow path for conducting a sample under investigation between said electrodes.

6. The detector of claim 4 including means for establishing an electric field for controlling the diffusion of said alkali compound through said permeable material.

7. A detector in accordance with claim 4 wherein said body comprises an elongated generally cylindrical hollow member and a closure member, and said heater means 0 includes a heater coil formed about said body.

8. A halogen vapor detector comprising:

an enclosed elongated tubular body of relatively narrow cross section which is sealed at opposite ends thereof and which defines a cavity for containing an alkali compound;

5 6 an alkali compound positioned in said cavity of said tubulation is formed as a coil of platinum and includes a container; carbon material positioned within said body. said body including a portion thereof formed of a ma- 1!. A detector in accordance with claim 9 wherein said terial which is permeable to vapors of the alkali tubulation contains a decomposable carbonaceous alkali compound; compound.

heater means adapted for causing said alkali compound 5 12. A detector in accordance with claim 11 wherein to vaporize and to thereby diffuse through said alkali said alkali compound comprises alkali alcoholate. permeable material; and,

means including first and second spaced-apart elec- References Cited trodes for establishing in a space between said elec- 10 UNITED STATES PATENTS trodes an electrical field and for indicating current 2 550 493 4 1951 Rice 324 33 flow between said electrodes, said tubular body posi- 2,979, 31 4 19 1 Moesta 324 33 tioned with respect to said electrodes for providing 3,372,994 3/1968 Giuffrida 23--254 introduction of dilfusing alkali vapors into the space 3,384,457 5/1968 Norell 23254 between said electrodes thereby enhancing current 15 3,439,262 4/1969 Roberts 32433 flow between the electrodes in the presence of a halogen vapcm MORRIS O. WOLK, Primary Examiner 9. A detector in accordance with claim 8 wherein said R, M, REESE, Assistant Examiner tubulation is of capillary dimension and is formed of platinum. 20 Us. 01. X.R.

10. A detector in accordance with claim 8 wherein said 23 232 

